Machine for correcting screw threads



April 8, 1958 v. L. Pr-:lcKu 2,829,471l

MACHINE FOR CORRECTING SCREW THREADS Filed oct. 27, 1954 v @sheets-sheet1.

LULU

E- if INVENTOR.

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April 8, 1958 v. PElcKu MACHINE FOR CORRECTING SCREW THREADS 5Sheets-Sheet 2 Filed Oct. 27, 1954 T IIIIFIP Je. m WP April 8, 1958 v.L. PElcKn MACHINE FOR CORRECTING SCREW THREADS 3 Sheets-Sheet 5 FiledOCT.. 27. 1954 NVENTOR. yasdfz'e Fez.' W7/ZL BY l 1 Mafvu MACHINE FORCORRECTING SCREW THREADS Vaisalie L. Peickii, SanMateo,iCalif.,'assignor to Micromatic Hone Corporation, Detroit, Mich.,a corporation i of Michigan `Application October 27, 1-954,` Serial No.464,999

` Z Claims. (Cl. 51--95) One object of the invention is to provide asimple,l

accurate means for correcting deficiencies in the lead,

thread-wobble and pitch-diameter occasioned by the previous matchiningoperations or heat treat deformation.

Another object is to provide `a means whereby the workpiece may bemounted for rotation about the generative axis of its helix, inspectedfor the locale and de gree of error; corrected, and re-inspected withoutdel mounting therefrom in the interim.

Another object is to provide a means whereby the vhelix of threadedcomponents may be ground or otherwise rna-` chinedwithout the use of alead-screw, sine-bar or other conventional means to procure the desiredhelix.

The overall invention consists of the principles shown and describedherein and in the co-pending application, Serial No.' 465,000, liledOctober 27, 1954, and assigned to the assigneeof the presentapplication, and the combination of elements and arrangement of parts asshown in the attached drawings; wherein:

Figure 1 is a plan view of a grinding or lapping machine embodying thefeatures of the present invention;

The machine as illustrated in the drawings consists of l a base plate 1on the rearward surface of which a precision grinding assembly generallyindicated at 45 is xedly mounted. The grinding assembly consists of apair of parallel head frames 2 atlixed to a supporting plate 1a which ismounted on base 1 for pivotalmovement about a center pin.2a. Adjustmentof screws 2b, which extend through arcuate slots in the supporting-plate1a, permits positioning of the grinding assembly so that the axis ofgrinding wheel 7 is at right angles to the workpiece helix. A forwardlyextending wheel arm 3 and a rearwardly extending stabilizer arm 4,formed as a unit, are pivotally mounted between the head frames 2 ontrunnions 5. The trunnions 5 ride on bearings 8 housed in the headframes 2 so as to afford a free tipping motion to the wheel arm 3. Agrinding wheel 7 is rotatably mounted on the forward end of the wheelarm 3 so as to be driveable by a drive motor 9 mounted on the wheel arm.A spring 6, bearing against the under surface of the stabilizer arm 4adjacent its rearward end, serves to force the grinding wheel 7 in adownward direction. The downward movement of the grinding wheel 7 islimited and may be regulated by a feed-adjusting screw 13 which ismounted on a xed bracket 10 and bears against a block 11 mounted on theupper surface of the stabilizer arm 4. A dial indicator 14, carried byan arm 12 iixedly secured to the bracket 10 above the stabilizer arm 4,registers the movement of the grinding wheel 7 as the feed-adjustingscrew 13 is backed oi.

United States Patent It may be seen that the grinding assembly abovedescribed provides the dressing tool for correcting threaded parts whichmay be precisely operated. The grinding wheel 7 may be raised or loweredto grind oi any desired amount of material. The dial indicator 14 beingthe same distance from the trunnions 5 as is the working surface of the`grinding wheel 7, the amount of moving of the stabilizer arm 4 below thedial indicator 14 will be identical to that of the wheel 7.

A block 15 is xedly mounted onthe base 1 below the grinding wheel 7 andisprovided with a transversely extending dovetail groove. A supportingblock 16 having a dovetail base portion is mounted on the block 15 withits dovetail base disposed in the dovetail groove of block 15. A setscrew 17 threaded into the supporting block 16 allows the block 16 to besecured in any desired longitudinally adjusted position along the block15. A supporting member 18 is mounted in the top of the block 16 andadjustably houses an upwardly extending followerlinger 19, thefollower-linger 19 lying directly below the axis of the wheel 7. Thelinger 19 has a tip 20 which conforms to the flank shape of the threadsof the workpiece, but is suciently truncated at its end to clear theroot of the helix. The tip 20 is iinely finished so as to closely iitthe Hank faces of the threads of the helix upon the pitch-diameterthereof. Finger 19 is vertically adjustable in its supporting member 18bymeans of set screw 21 to accommodate workpieces of varying size.Furthermore, the linger 19 may be rotated toconform to threads ofvarying pitch. e

A V-block 22 is tixedly mounted on the base 1 in parallel relation tothe axis of the wheel 7, and has a` plurality of balls 23 mountedtherein which form a frictionless guideway for a workholding carriage,generally indicated `at 40. The workholding carriage is formed as aseparate unit and includes a supporting bar 24 and two `is movable alongthe generative axis. of its threads past the grinding wheel.

The workpiece is provided with pivot ends 30 and 30a, preferably formedintegrally with the workpiece, and centered onthe generative axis of thethreads of the workpiece. The workpiece is mounted with its pivot ends30 and 30a disposed in the work centers 27 and 28 so as to be freelyurotatable therebetween about the generative axis of its threads.

One pivot end 30a is provided with a pinion 31 which is dogged theretofor mutual rotation with the workpiece. A motor 32 is mounted ontransverse arm 26 and is provided with a gear 33 fast on the end of itsdrive shaft. The gear 33 engages an intermediate gear 34 rotatablysupported on the transverse arm 26, which in turn en gages the pinion 31whereby the workpiece may be rotated. As will be apparent to thoseskilled in the art, any suitable driving means such as belt and pulleymay be used to drive the workpiece in rotation.

It may be seen that the preponderance ofweight is on the ends of thetransverse arms adjacent the grinding wheel and therefore the entireworkholding carriage will tend to tip downwardly at that end. However,the follower-linger 19 which engages the threads of the workpiecesupports the workholding carriage in an upright position. As the motor32 is driven, the rotation of the workpiece will feed thethread onto thefixed linger V19, moving the workpiece along its axis. Because thesupporting bar rests freely on the balls 23 the entire workholdingcarriage is free to move with the workpiece. It should also be notedthat the workholding carriage, along with the workpiece, forms anintegral unit which may be freely removed from the rest of the machinein order to examine or inspect the workpiece. The workpiece itself neednot be removed from the carriage on which it is xtured. This integralunit is common with that shown in my copending application abovedescribed and has utility therewith.

In the operation of the machine the block 16 is adjusted so that thefinger 19 is disposed in a thread groove slightly in back of thegrinding wheel and is adjusted in height so that the transverse arms 25and 26 lie in'a substantially level plane. Since the purpose of themachine is primarily to correct error in a machined or ground helix ofthe workpiece, it is desirable vthat the pitch diameter of the latter beprovided slightly oversize prior to this operation. In this manner thehelix can be exactly nished to its proper specications. Thefeed-adjusting screw 13 is adjusted so as to bring the wheel 7 intoproximity with its adjacent thread groove. The follower-finger 19 isthen adjusted to center the peripheral edges of the wheel in a neutralportion of the thread groove; that is to say, to a position where thereis similar clearance between the thread flanks of the workpiece andthetwo grinding surfaces of theV wheel.

In an operation where extremely precise dimensions are required, amagnifying glass or microscope may be used, as is shown schematically at36. This facilitates observations during the above-describedadjustments. The motors 9 and 32 are then started and the feed screw 13is further adjusted to lower the grinding wheel into its adjacent threadgroove. The degree of infeed of the wheel is indicated on the dial gauge14 which maybe set at its zero point at any time by the operation ofscrew 37 which is threaded through the block 11 into engagement with anextensible rod 38 which form part of the gauge 14. As the workpiece isrotated the threads are caused to advance by the finger 19, which feedthe entire length of thread past the grinding wheel 7. At the end ofeach .pass of the complete screw length, the feed motor 32 may bereversed to conveniently repeat the grinding operation by movement ofthe workpiece in the opposite direction. However, it is usually foundadvantageous to check the condition of the workpiece after each grindingpass, This procedure requires the retraction of the grinding wheel, theremoval of the carriage from the machine and its transfer to thecompanion inspection instrument covered by my copending applicationmentioned above.

This periodic removal of the carriage, with the workpiece intact,enables convenient and precise checking of the condition of the helixand the determination of where additional corrective treatment may beneeded thereon. In practice, it has been found that by adjusting thegrinding wheel and follower-finger as the need is indicated by mychecking device, this machine has produced screw threads, and otherhelical forms, of extreme precision, even when manipulated by arelatively unskilled operative.

It will thus be seen that this invention provides a simple, economicaland effective means for correcting the geometry of screw threads and thelike helices; and that the method herein described, of periodicinspection of the workpiece while still fixtured on its generative axis,avoids the need for taking into account the probability of error usuallypresent whenever refixturing is required.

What is claimed is:

l. In a machine for dressing a thread on a workpiece, a base, a supporton said base, a lever pivotally mounted on said support between the endsof said lever, one portion of said lever having a dressing tool mountedthereon, the opposite portion of said lever having adjusting meansthereon by which said lever is rocked, ball means supported on saidbase, a carriage mounted on said ball means having on the portionthereof adjacent to said dressing tool supporting means for theworkpiece, the preponderance of weight of said portion causing saidcarriage to tilt downwardly away from the dressing tool, and a fingeradjustably mounted on said base engageable with a portion of the threadengaged by said tool for tilting the carriage and adjusting theworkpiece toward said tool, said carriage and workpiece forming a unitwhich is removable as a unit from the finger and ball means on saidbase.

2. In a machine for dressing a thread on a workpiece, a base, a supporton said base, a lever pivotally mounted on said support between the endsof said lever, one por-V tion of saidflever having a dressing toolmounted thereon, the opposite portion of said lever having adjustingmeans thereon by which said lever is rocked, ball means sup,- ported onsaid base, a carriage mounted on said ball means having on the portionthereof adjacent to said dressing tool supporting means for theworkpiece, the preponderance of weight of saidA portion causing saidcarriage to tilt downwardly away from the dressing tool, a\ iingeradjustably mounted on said base engageable with a portion of the threadengaged by said tool for tilting the carriage and adjusting theworkpiece toward said tool, and driving means for said workpiece whichproduces the rotation thereof and also the longitudinal movement due tothe engagement of said finger with said thread portion.

References Cited in the tile of this patent UNITED STATES PATENTS1,782,154 Thomas Nov. 18, 1930 2,088,538 Solomon July 27, 1937 2,122,184Scrivener June 28, 1938

